Fix placeholderTextColor not supported below Qt 5.12

resources/qml/MessageInput.qml

@@ -122,7 +122,14 @@ Rectangle {
                 text: "asfkajsdf"
                 selectByMouse: true
                 placeholderText: qsTr("Write a message...")
-                placeholderTextColor: colors.buttonText
+                //placeholderTextColor: colors.buttonText
+		// only set the anchors on Qt 5.12 or higher
+		// see https://doc.qt.io/qt-5/qml-qtquick-controls2-popup.html#anchors.centerIn-prop
+		Component.onCompleted: {
+			if (placeholderTextColor !== undefined)
+			placeholderTextColor = colors.buttonText
+
+		}
                 color: colors.text
                 width: textInput.width
                 wrapMode: TextEdit.Wrap